A conventional pneumatic tool such as a sander as shown in FIG. 1 includes a sander tool T rotatably secured with a shaft of a rotor R driven by an incoming compressed air source through an air inlet passage I formed in a grip G, and an exhaust pipe E connecting to a hood encasing the sander tool T with a hose H connected to a collection bag C for the collection of dust which is produced from the area performing a rotational sanding operation by the tool T, and a Venturi tube V formed in the exhaust pipe E adjacent to a by-pass branch B for directing a by-pass inlet compressed air stream from the branch B for drafting a dust-laden exhaust air stream through the pipe E and hose H for dust removal providing a clean working environment.
However, such a conventional rotary pneumatic tool has the following drawbacks:
1. Since a by-pass incoming compressed air stream is directed through the branch B for effecting the vacuum drafting in the exhaust pipe E, the main air flow rate for driving the rotor R of the air motor will be reduced to decrease the output power of the sander T, thereby reducing the motor efficiency and its productivity.
2. An additional exhaust pipe E should be provided to connect the hood of the sander tool T to a dust-collection hose H to thereby increase an installation cost and also increase operational inconvenience for handling such a cumbersome assembly.
3. The operating (sanding) end, i.e., the sander tool T, is rotatably mounted on a lower end of the rotor shaft remotely positioned from the rotor end which may therefore cause unbalancing or torsional vibration when running the air motor. The unbalanced or vibrational operation of the conventional pneumatic tool may waste mechanical energy of the pneumatic system and may easily cause operator fatigue or even negatively influence his (her) occupational health.
Although a balancer may be further provided for overcoming such a vibrational shortcoming of the air tool, an additional installation of the balancer may increase equipment volume and weight of the tool, still influencing its handling and operation as well as its esthetic appearance.